Simulation scaling with DFT and non-DFT

ABSTRACT

Electronic design automation modules for simulate the behavior of structures and materials at multiple simulation scales with different simulation modules.

REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit U.S. Application No.61/883,158 filed Sep. 26, 2013; and U.S. Application No. 61/883,942filed Sep. 27, 2013; and U.S. Application No. 61/889,355 filed Oct. 10,2013, incorporated by reference herein.

The following patent applications are incorporated by reference herein:International Application No. PCT/US2014/057840, titled “PARAMETEREXTRACTION OF DFT” filed Sep. 26, 2014; and U.S. Application No.14/498,492, titled “ITERATIVE SIMULATON WITH DFT AND NON-DFT” filed Sep.26, 2014.

BACKGROUND Field of the Invention

The present invention relates to electronic design automation, andmodules for simulating the behavior of structures and materials atmultiple simulation scales with different simulation modules.

SUMMARY

One aspect of the technology is an EDA tool comprising a data processor;and storage configured to provide computer program instructions to theprocessor.

The storage includes a controller module causing a plurality ofsimulation modules to perform an EDA simulation at a plurality ofdifferent simulation scales. The plurality of simulation modules includea first set of one or more ab initio simulation modules simulating afirst volume with a first boundary, and a second set of one of morenon-ab initio simulation modules simulating a second volume with asecond boundary. The second volume is larger than the first volume.

The controller module causes, responsive to a simulated volume occupiedby a nonzero part of a simulated property being a larger percentage ofthe second volume than the first volume, switching from the second setof one or more non-ab initio simulation modules to the first set of oneof more ab initio simulation modules.

In one embodiment, the simulated property as simulated by the first setof one or more ab initio simulation modules is equal at the firstboundary to an asymptotic value of the simulated property.

In one embodiment, the simulated property as simulated by the second setof one or more ab initio simulation modules is equal at the secondboundary to an asymptotic value of the simulated property.

In one embodiment, the simulated volume fits within the first volume.

In one embodiment, the first set of one or more simulation modulesincludes a density functional theory module, and the second set of oneor more simulation modules excludes the density functional theorymodule.

Another aspect of the technology is a computer-implemented methodcomprising:

causing a plurality of simulation modules to perform an EDA simulationat a plurality of different simulation scales, the plurality ofsimulation modules including:

a first set of one or more ab initio simulation modules simulating afirst volume with a first boundary; and

a second set of one of more non-ab initio simulation modules simulatinga second volume with a second boundary, the second volume larger thanthe first volume; and

causing, responsive to a simulated volume occupied by a nonzero part ofa simulated property being a larger percentage of the second volume thanthe first volume, switching from the second set of one or more non-abinitio simulation modules to the first set of one of more ab initiosimulation modules.

Various embodiments are disclosed herein.

One aspect of the technology is an EDA tool comprising a data processor;and storage configured to provide computer program instructions to theprocessor.

The storage includes a controller module causing a plurality ofsimulation modules to perform an EDA simulation at a plurality ofdifferent simulation scales. The plurality of simulation modulesincludes a first set of one or more ab initio simulation modules of afirst volume with a first boundary; and a second set of one of morenon-ab initio simulation modules of a second volume with a secondboundary, the second volume larger than the first volume.

The controller module causes the first set of one or more ab initiosimulation modules to perform the EDA simulation of a simulatedproperty, and depending on whether a nonzero magnitude of an error ofthe simulated property exceeds an error threshold, the controller modulecauses one of: (i) switching from the first set of one or more ab initiosimulation modules to the second set of one of more non-ab initiosimulation modules, and (ii) remaining with the first set of one or moreab initio simulation modules despite the error.

In one embodiment, the error is a nonzero difference between:

(i) the simulated property at the first boundary simulated by the firstset of one or more ab initio simulation modules, and

(ii) an asymptotic value of the simulated property beyond the firstboundary.

In one embodiment, the asymptotic value is obliquely asymptotic.

In one embodiment, the asymptotic value is horizontally asymptotic.

In one embodiment, the asymptotic value is vertically asymptotic.

In one embodiment, the first set of one or more simulation modulesincludes a density functional theory module, and the second set of oneor more simulation modules excludes the density functional theorymodule.

Another aspect of the technology is a computer-implemented methodcomprising:

causing a plurality of simulation modules to perform an EDA simulationat a plurality of different simulation scales, the plurality ofsimulation modules including:

a first set of one or more ab initio simulation modules of a firstvolume with a first boundary; and

a second set of one of more non-ab initio simulation modules of a secondvolume with a second boundary, the second volume larger than the firstvolume; and

causing the first set of one or more ab initio simulation modules toperform the EDA simulation of a simulated property, and depending onwhether a nonzero magnitude of an error of the simulated propertyexceeds an error threshold, causing one of: (i) switching from the firstset of one or more ab initio simulation modules to the second set of oneof more non-ab initio simulation modules, and (ii) remaining with thefirst set of one or more ab initio simulation modules despite the error.

Various embodiments are disclosed herein.

Other aspects and advantages of the present technology can be seen onreview of the drawings, the detailed description and the claims, whichfollow.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of various simulation modules at multiplesimulation scales coupled together and using output of one module asinput for another module, and automatically executing another module atthe same simulation scale or different simulation scale to improveinaccurate input (such as missing input).

FIG. 2 is an example block diagram of simulation modules at multiplesimulation scales coupled together via an intermediate module usingoutput of an ab initio simulation module as input for a higher scalesimulation module

FIG. 3 is an example block diagram of simulation modules at multiplesimulation scales coupled together via an intermediate module usingoutput of a higher scale simulation module as input for an ab initiosimulation module.

FIG. 4 is an example block diagram of simulation modules at multiplesimulation scales coupled together via intermediate module processing,to iterate between an ab initio simulation module and a higher scalesimulation module.

FIG. 5 is an example process flow of executing simulation toolsautomatically at multiple simulation scales, to improve inaccurate input(such as missing input).

FIG. 6 shows different simulation volumes of simulation modules atdifferent simulation scales.

FIGS. 7-8 shows a switch between simulation modules at differentsimulation scales, from a larger simulation volume to a smallersimulation volume.

FIGS. 9-10 shows a switch between simulation module volumes, withhorizontal and oblique asymptotes.

FIGS. 11-12 show an error at the border between simulation modules atdifferent simulation scales, from a smaller simulation volume to alarger simulation volume.

FIGS. 13A, 13B, 13C and 13D illustrate various lattice configurations,as examples of arrangements in which a semiconductor property has afinite distortion range.

FIG. 14 is a simplified block diagram of a computer system configured toperform IC simulation at multiple scales.

FIG. 15 illustrates EDA tools and process flow for integrated circuitdesign and manufacturing.

DETAILED DESCRIPTION

A detailed description of embodiments of the present invention isprovided with reference to the Figures.

As processing power increases sufficiently, scaling tools can simulatetransistor behavior at increasingly granular levels, even at the atomiclevel. A trade-off exists among granularity of the simulation, andrequired computation resources. For example, fine granularity increasesrequired computation resources, and so tends to have reduced simulationvolume. In another example, coarse granularity reduces computationresources, and so tends to have enlarged simulation volume.

There are many levels of how detailed the physical model can be.Typically, simpler models can handle larger examples whereas moresophisticated models typically can only handle a smaller subset of suchexamples within comparable computation time. For example, so-calledcompact transistor models like BSIM represent a transistor as severalempirical formulas that can be calculated within milliseconds. Thisenables such compact models to be used in characterizing large circuitsthat contain thousands of transistors. A more sophisticated TechnologyComputer-Aided Design (TCAD) model represents transistor as hundreds ofthousands of interconnected points that are scattered throughoutdifferent parts of the transistor. Several key Partial DifferentialEquations (PDEs) are solved on these interconnected points and determinedistribution of the charges and electrostatic potential throughout thetransistor, as well as the charge transport between the terminals. TheTCAD model typically handles a handful of transistors (say, from 1 to 5)in the same timeframe as the compact model handles thousands oftransistors in a circuit. The upside for the TCAD model is that it canpredict transistor behavior based on the known material properties,whereas the compact model typically needs to be calibrated either toTCAD model or to experiments. Yet another modeling level is DensityFunctional Theory (DFT), which typically cannot represent an entiretransistor, but represents a small part of it, considering each atomseparately and how the atoms are connected to each other. A collectionof atoms of the order of 100 hundred, which is less than one percent ofthe atoms in a transistor, can be characterized by DFT in the sametimeframe as TCAD handles a few transistors and the compact modelhandles a thousand transistors. The DFT model can predict materialproperties based on the atomic properties, and therefore can provide theinput for the TCAD model to characterize the transistor. So, there is ahierarchy of modeling approaches, including DFT (sometimes referred toas “first principles” approach), TCAD, and compact models. The tools inthis hierarchy are applied sequentially, going from detailedphysics/small structure towards the simpler physics and larger size, andusually this works fine. However, there are cases where thishierarchical approach fails, and there are more such cases as thetransistor scaling continues. There are some characteristics thattypically can be obtained only with large enough structure size. Forexample, typically one can only get accurate electric field distributionand the current crowding/filamentation effects on transistor scale, i.e.a TCAD level model. Such characteristics can affect the inter-atomicbonds and the band structure, and therefore alter results of DFTanalysis that cannot calculate such characteristics on the scale it canhandle. The present approach bridges this gap.

FIG. 1 is a block diagram of various simulation modules at multiplesimulation scales coupled together and using output of one module asinput for another module, and automatically executing another module atthe same simulation scale or different simulation scale to improveinaccurate input (such as missing input). Details of the blocks arediscussed in U.S. Provisional Application 61/883,158 filed Sep. 26,2013; and U.S. Application No. 61/883,942 filed Sep. 27, 2013; and U.S.Application No. 61/889,355 filed Oct. 10, 2013, incorporated herein byreference.

This technique adaptively combines multiple simulation and designmodules and methodologies, in order to offer automated, self-adaptive,and multi-scale simulation capabilities of various physical processes inthe fabrication and operation of integrated circuit devices. The modulescan include several hierarchical simulation modules, each of whichfocuses on the physical processes in one particular spatial scale. Themodules can communicate in one direction, or back-and-forth with eachother via parameter extraction in an automated and self-adaptive way.

The multiple modules can have one or more of multiple benefits. Firstly,multiple modules offer systematic and comprehensive simulationcapabilities of the physical processes in multiple spatial scales. Whilethe existing simulation methodologies focus on the physical processes inone particular spatial scale, the modules include them as internalmodules or at least modules communicating via an intermediate module,and offer systematic simulation functionalities in multiple spatialscales. Secondly, the modules help reducing the cost of experiment andtesting by including ab initio simulations modules as the internalmodules, or as external modules in communication via an intermediatemodule, which can offer valuable physical insights and replace empiricalexperiments and calibrations. Thirdly, the modules can significantlyreduce computational time and consumption of computational resources, byreplacing some computationally expensive calculations via parameterextraction. Fourthly, the modules are able to control the simulationautomatically and self-adaptively, hence minimizing the needs of humancontrol and intervention.

Without the modules, one needs to be an expert of many sophisticatedsimulation modules and methodologies, to perform simulations of physicalprocesses which span multiple spatial scales. The simulations performedin this fashion are functionality limited, physical expertise demanding,computationally expensive, human time intensive, and error prone. Themodules are dedicated to solve these problems.

Example modules shown in FIG. 1 include: quantum Monte Carlo (QMC) 19;time-dependent density functional theory (TD-DFT) 15; density functionaltheory (DFT), DFT with on-site U (DFT+U) 14, and dynamic mean fieldtheory (DMFT) 14; ab initio molecular dynamics (AIMD) 18; tight binding(TB) 13; classical molecular dynamics (MD) 17; Monte Carlo (MC) 16;non-equilibrium Green's function (NEGF) 12; Wigner and wave functionformalism quantum transport 21; quantum and deterministic Boltzmanntransport 10; and various continuum simulation modules and methodologies(continuum), etc.

Example information flows between the different modules, are follows:

The QMC module solves the many-body physics problems. The electronicstructure and lattice structure properties calculated from QMC are theoutput of the modules. Since the mean field theory methodologies DFT andTD-DFT sometimes give imprecise results (e.g. band structure, band gap,etc.), the QMC module can verify the results. Similarly, the QMC modulecan benchmark the MD, AIMD, TB, MC, NEGF, and continuum modules, tosimulate the atomic movement, transport properties, and various deviceperformance metrics.

The TD-DFT module solves the time dependent Schrodinger equation. Thevarious optical response properties of materials and the atomic movementunder external excitation can be obtained from the TD-DFT module. Sincethe DFT may not account for electronic excitation, the TD-DFT module canbenchmark DFT results when the electronic excitation cannot be ignored.The inter-atomic force computed from TD-DFT is used in the AIMD and MDmodules to obtain the atomic trajectory. The optical response relatedparameters used in the MC, NEGF, and continuum modules are computed fromthe TD-DFT module.

The DFT module can include not only the DFT modules based on mean fieldtheory and single particle approximation, but also strong correlationsimulation algorithms like DMFT and DFT+U. The DFT module can generatethe electronic structure. The inter-atomic forces computed in the DFTmodule is used to calculate the atomic movement in the AIMD module. Theenergy calculated in the DFT module is used to generate empirical forcefields, which can be used in the MD module, by using methods likeparameter fitting and/or optimization algorithms. The variousphenomenological parameters in the TB, MC, and continuum modules arecalibrated and optimized using batch calculations in the DFT module. TheHamiltonian and overlap matrices in the NEGF module can be obtained fromthe DFT module.

DFT is an example of a class of approaches known as “ab initio” or“first principles” approaches. Such approaches require minimal empiricalinput to generate accurate ground state total energies for arbitraryconfigurations of atoms. These approaches make use of fundamentalquantum mechanical equations, and require very little in the way ofexternally-supplied materials parameters. This capability makes thesemethods well-suited to investigating new materials and to providinghighly detailed physical insight into material properties and processes,but also renders them extremely computation intensive. As such, a taskcontrol system can control a multi-scale simulation project in which anyof the ab initio approaches is used in combination with less computationintensive approaches such as 2D Schrödinger and TCAD. As used herein, an“ab initio” or “first principles” analysis approach or module is anapproach or module that develops its results at least in part by solvingSchrödinger's equation based on positions and types of atoms. Otherexample first principles approaches that can be used herein include EPM(Empirical Pseudo-potential Method) modules, and ETB (Empirical TightBinding) modules, and combinations of approaches.

The TB module is based on phenomenological expressions of variousphysical quantities. It can be used to compute electronic and transportproperties. The inter-atomic forces calculated in the TB module can beused to generate the force field in the MD module. The TB description ofthe target system (e.g. Hamiltonian) is used in the MC, NEGF, andcontinuum models to obtain the physical properties pertaining toelectron transport and device process.

The NEGF module computes the transport properties, which are the outputof the modules. The NEGF module can simulate not only transport withscattering, but also ballistic transport. So it can be used to benchmarkthe continuum module, especially when the transport is largelyballistic. Also, the physical properties (local density of states,transmission, mean free path, etc.) obtained from the NEGF module canoffer valuable insights in the ultra-scaled devices. NEGF iteratesbetween (i) the Poisson equation to get a 3D potential profile U, and(ii) the NEGF transport equation to get a density matrix rho. NEGF alsogenerates the following distributions: electron charge density, holecharge density, electron velocity, hole velocity, electrostaticpotential, current (product of respective charge density and chargevelocity).

The MC module includes, but is not limited to, device MC, kinetic MC,and lattice kinetic MC. The device operation physics and fabricationprocess are the output of the MC module. The MC module can take theoutput from other modules as input. For example, the energy dumped bythe DFT module can be used to estimate the activation energy in the MCmodule to evaluate the atomic migration probability. The MC module iscapable of simulating many physical processes, e.g. dopant diffusionduring process, electron transport, atom migration, etc.

The quantum and deterministic Boltzmann module relies on the Boltzmannequation for calculation of transport properties.

The Wigner and wave function formalism module calculates quantumtransport properties.

The continuum module accepts output of the other modules and use them asinput, to calculate various device performance metrics, like chargedistribution, current-voltage curve, etc. The continuum module includesvarious numerical algorithms like finite element method, finite volumemethod, finite difference time domain method, boundary element method,etc. The continuum module can be considered an intermediate module thatcommunicates between different modules.

The coordination module coordinates the other modules. If a particularmodule has missing input, the coordination module executes anothermodule to provide the missing input. If a particular simulation scale isnot specified in the execution instruction, the coordination moduledetermines the appropriate scales to run. The proposed modules receivetarget simulation quantities via a user interface, and instruct thecoordination module to start the simulation. After receiving thesimulation instructions, the coordination module decides whichfunctional block(s) should be called to perform these simulation tasks.To accomplish the entire user request, the functional blocks of theproposed module may be called many times adaptively and iteratively bythe coordination module. The communication of information (likeparameter request and extraction) between/among the functional blocks iscontrolled by the coordination module. The coordination module can beconsidered an intermediate module that coordinates different modules.

A particular simulation module can be integrated into a suite ofmultiple simulation modules. Alternatively, intermediate modules canprocess output from discrete simulation modules for use as input by eachother.

In one example division of different simulation scales, a completesemiconductor device scale includes SPICE and other continuum modules.The ab initio simulation scale can include AIMD, DFT, DMFT, DFT+U,TD-DFT, and QMC. The intermediate simulation scale can include MC, NEGF,MD, and TB. Drift-diffusion can be a large scale. Different simulationsscales can be viewed also as a continuum of scales, with finergradations of scale, such that any pair of tools can have overlapping ornon-overlapping simulation volumes.

FIG. 2 is an example block diagram of simulation modules at multiplesimulation scales coupled together via an intermediate module usingoutput of an ab initio simulation module as input for a higher scalesimulation tool. To take advantage of the accuracy of more granularsimulation, and the lowered computation intensity of less granularsimulation, parameters are passed between multiple levels of simulation.

One such combination uses DFT to develop inputs for NEGF, and uses NEGFto simulate larger volumes than would be possible with DFT alone.

At 22, results are produced from an ab initio simulation module such asDFT. At 24, results are processed into higher simulation scale input.Processing can be as minimal as passing a parameter, or performingmultiple operations to extract data. At 26, the simulation is continuedusing the results from the ab initio simulation module as input of anintermediate scale simulation module such as NEGF.

DFT receives input such as types and coordinates of all atoms thatcomprise the structure, coordinates of additional electrons and holes,and boundary conditions of electrostatic potential. DFT generates asoutput, band structure, bandgap Eg, Young modulus E, Poisson ratio v,hole and electron effective mass m*, permittivity, into larger scalesimulations. For example, NEGF can directly use this output as theHamiltonian. TCAD can adjust the mobility with this output. SPICEparameters can be adjusted with this output.

One DFT embodiment performs the simulation with only internal fields orpotential barriers. Another DFT embodiment performs the simulation withan external field output from NEGF or other higher scale modules.

The scheme can offer one or more of multiple benefits. (1) It enablesthe calculation of large systems which are too computationally expensivefor the ab initio simulation modules. (2) It enables simulation of thephysical process whose duration is too long for the ab initio simulationmodules. (3) It enables batch simulations of a large number of systemswhich are too computational resource consuming for the ab initiosimulation modules. (4) It improves the calculation precision of thephenomenological simulation modules and methodologies by adaptivelyextracting parameters from the comparatively more accurate ab initiosimulation modules. (5) It offers automated and self-adaptivecalculation scheme, which minimizes needs of human intervention andmaximizes productivity of simulation and design.

Without the scheme, one typically needs to perform the parameterextraction process based on prior simulation experience and intuition,which are not only human time intensive but also error prone. Thisscheme solves this problem, by automating the parameter extraction fromthe ab initio simulation modules with an intermediate module, and usingthe extracted parameters in the phenomenological simulation modules.

The ab initio scale simulation modules and methodologies mentioned abovecan include, but are not limited to, the following modules: quantumMonte Carlo (QMC), time dependent density functional theory (TD-DFT),density functional theory (DFT), and ab initio molecular dynamics(AIMD), etc.

The intermediate scale phenomenological simulation modules andmethodologies” mentioned above include, but not limited to, thefollowing modules: classical molecular dynamics (MD), Monte Carlo (MC),tight-binding (TB), non-equilibrium Green's function (NEGF), andcontinuum simulation methods. Different simulations scales can be viewedalso as a continuum of scales, with finer gradations of scale, such thatany pair of tools can have overlapping or non-overlapping simulationvolumes.

The intermediate module extracts parameters from ab initio densityfunctional theory (DFT) simulations. The extracted parameters can beused as the inputs of other modules (e.g. Monte Carlo), to facilitatemulti-scale simulations. Example applications of the DFT intermediatetool output are: capacitance calculator, circuit simulator forsimulation operation of a circuit of devices, device simulator forcomputing current-voltage in one device or combination of devices,device simulator based on the solution of partial differentialequations, device simulator based on the solution of the Boltzmanntransport equation, device simulator based on quantum transport, anddevice simulator for the simulation of magnetic based devices.

Multi-scale simulation assists downscaling integrated circuitsemiconductor devices and exploration of novel materials. Downscalingmakes the quantum mechanical effects more important. The new moduleshelp understand new materials' properties and help improve the devicedesign. Users can simulate the devices by combining the ab initioquantum mechanical simulations from first-principles.

One of the most mature and widely-applied ab initio algorithms is thedensity functional theory (DFT). Simulation modules, such as DFTmodules, can be internal to the EDA tool, or an external module by athird party. Examples of DFT tools are VASP, SIESTA, Quantum Espresso,OpenMX, etc.

The physical semiconductor quantities extracted from DFT discussed belowin more detail include: bandgap (direct and indirect), effective massscalar, effective mass tensor, non-parabolicity, and N-band k.p modelparameters (such as Luttinger parameters). Although the example belowdiscusses 6-band k.p model Luttinger parameters, other embodiments aredirected to various numbers of bands (e.g., 2, 6, 8, 20, etc.). Suchpreceding parameters can be calculated in different directions such asx, y, and z due to anisotropic behavior. These quantities can be used asthe input parameters of other tools.

To extract the bandgap, the intermediate module relies on input ofmultiple k points, such as k1 (k1x, k1y, k1z) and k2 (k2x, k2y, k2z).Here, k1 specifies the conduction band maximum (CBM) location, and k2specifies the valence band minimum (VBM) location.

The intermediate module parses the DFT output data, to locate these twok points in the DFT data. Using the Fermi level, intermediate modulewill automatically determine from which band the eigenvalues E(k1) andE(k2) are extracted. Finally, the result of E(k2)−E(k1) is used as thebandgap value.

The intermediate module can perform data interpolation. Alternatively,it parses DFT data and directly locates E(k1) and E(k2). The two kpoints can be specified when performing the DFT calculations, such thatE(k1) and E(k2) are explicitly contained in the DFT data.

To extract the effective mass tensor, the intermediate module uses threequantities: the band label (which band to compute effective masstensor), the band structure valley location ko(kox, koy, koz) in theBrillouin zone, and the cutoff value kcut.

Then, the intermediate module performs the extraction calculations. Theintermediate module parses the DFT output data and chooses all k pointsk(kx, ky, kz) which can satisfy√{square root over ((k _(x) −k _(ox))²+(k _(y) −k _(oy))²+(k _(z) −k_(oz))² <k _(cut))}

Then, using the band label specified, the eigenvalues E(k), includingE(ko), corresponding to the chosen k points in the target band are readout from DFT data.

Then, the effective mass tensor mij (i, j=x, y, z) extraction isperformed based on the Taylor expansion of the E(k) relation near ko

${E(k)} = {{E\left( k_{0} \right)} + {\frac{\hslash^{2}}{2}{m_{ij}^{- 1}\left( {k_{i} - k_{oi}} \right)}\left( {k_{j} - k_{oj}} \right)} + {O\left( {{\Delta\; k}}^{2} \right)}}$

To obtain the numerical values of the effective mass tensor, which hasmultiple (e.g., six) independent components due to symmetry mij=mji, thelinear algebraic equations A X=B is formulated and solved, where A is ann×6 matrix; B and X are 6×1 matrices; and n is the number of chosen kpoints. The solution of the A X=B is based on least square solutionalgorithm. The effective mass tensor matrix inversion is calculated.

Therefore, appropriate DFT data such as the kcut value are provided tointermediate module, such that there are sufficient (e.g., 6) linearlyindependent equations in A X=B. Otherwise, the extraction can crash orgive unphysical results.

Also, kcut can be set as an appropriate value. If small enough, allchosen (kx, ky, kz) points are in the parabolic region near (kox, koy,koz). Secondly, if kcut is large enough, the difference E(k)−E(ko) islarge enough to ensure extraction accuracy. Although an examplekcut=0.01 can be used, kcut is a material-specific parameter to becustomized.

To extract the effective mass scalar, the intermediate module uses threeinputs: the band label (which band to compute effective mass scalar),the band structure valley location ko(kox, koy, koz) in the Brillouinzone, and another k point kp(kpx, kpy, kpz) near ko.

The intermediate module parses the DFT data and find out the eigenvaluesE(kp) and E(ko) in the specified band. Then, using the Taylor expansionof the E(k) relation at ko

${E\left( k_{p} \right)} = {{E\left( k_{0} \right)} + {\frac{\hslash^{2}}{2m}{{k_{p} - k_{o}}}^{2}} + {O\left( {{\Delta\; k}}^{2} \right)}}$

the effective mass scalar m along the direction kp−ko can be computed.

Similar to the effective mass tensor extraction, the |kp−ko| can besmall enough such kp that is still in the parabolic region of thevalley. And it can be large enough such that the difference E(kp)−E(ko)is large enough to ensure extraction accuracy.

To extract the non-parabolicity parameter α, the intermediate modulerelies on multiple inputs: the band label (which band to computeeffective mass scalar), the band structure valley location ko(kox, koy,koz) in the Brillouin zone, a k point kp(kpx, kpy, kpz) in the parabolicregion near ko, and a k point kn(knx, kny, knz) in the non-parabolicregion far away from ko.

To extract non-parabolicity, in the first step, the effective massscalar m along the direction kp−ko is computed as described. Using thevalue of m,

${E_{p}\left( k_{n} \right)} = {{E\left( k_{0} \right)} + {\frac{\hslash^{2}}{2m}{{k_{n} - k_{o}}}^{2}}}$is computed to obtain the eigenvalue at kn if the band structure wereparabolic. Actually the band structure is non-parabolic at kn, so in thesecond step, using

${E({kn})} = {{\frac{1}{2 \propto}\left\lbrack {{- 1} + \sqrt{1 + {4\left\lbrack {{{{Ep}({kn})} - {E({ko})}} \propto} \right\rbrack}}} \right\rbrack} + {E({ko})}}$

the non-parabolicity parameter α is computed.

The choice of kp follows the principles introduced in effective massscalar extraction. The choice kn can be pre-specified or up to the user,provided that kn is in the non-parabolic region.

To extract the k.p model parameters, the user or intermediate moduleprovides two inputs to the intermediate module: the location of the bandstructure valley ko(kox, koy, koz) in the Brillouin zone, and the cutoffvalue kcut.

The intermediate module extracts the k.p model parameters in multiplesteps. In the first step, it parses the DFT data and select the k pointsk(kx, ky, kz) whose distances to ko are smaller than kcut. Also, thecorresponding eigenvalues EDFT(k) in the highest six valence bands areread from DFT data.

In the second step, the initial guess of the model parameters (γ1, γ2,γ3, and Δso) is used to generate the 6×6 Hamiltonian matrix

$H = \begin{bmatrix}{P + Q} & {- S} & R & 0 & {{- S}/\sqrt{2}} & {\sqrt{2}R} \\\; & {P - Q} & 0 & R & {{- \sqrt{2}}Q} & {\sqrt{3/2}S} \\\; & \; & {P - Q} & S & {\sqrt{3/2}S^{*}} & {\sqrt{2}Q} \\\; & \; & \; & {P + Q} & {{- \sqrt{2}}R^{*}} & {{- S^{*}}/\sqrt{2}} \\\; & \; & \; & \; & {P + {\Delta\;{so}}} & 0 \\\; & \; & \; & \; & \; & {P + {\Delta\;{so}}}\end{bmatrix}$ where $\left\{ \begin{matrix}{P = {\frac{\hslash^{2}}{2m_{e}}{\gamma_{1}\left( {k_{x}^{2} + k_{y}^{2} + k_{z}^{2}} \right)}}} \\{Q = {\frac{\hslash^{2}}{2m_{e}}{\gamma_{2}\left( {k_{x}^{2} + k_{y}^{2} + k_{z}^{2}} \right)}}} \\{R = {\frac{\hslash^{2}}{2m_{e}}{\sqrt{3}\left\lbrack {{- {\gamma_{2}\left( {k_{x}^{2} - k_{y}^{2}} \right)}} + {2i\;\gamma_{3}k_{x}k_{y}}} \right\rbrack}}} \\{S = {\frac{\hslash^{2}}{2m_{e}}2\sqrt{3}\left( {k_{x} - {ik}_{y}} \right)k_{z}}}\end{matrix} \right.$

according to the k.p theory. Here, m_(e) is the electron mass; γ1, γ2,γ3 and are the Luttinger parameters; and Δso is the spin-orbit split-offenergy. Then, the eigenvalue problemH(k)X(k)=EBKP(k)X(k)

is solved, using the ZGEEV subroutine as implemented in LAPACK package,to obtain the eigenvalues (e.g., 6) for each selected k point.

In the third step, the difference between the EDFT(k) and the EBKP(k) isevaluated using the cost function, which is defined as

$c = \sqrt{\frac{1}{N_{k}}{\sum\limits_{k}^{\;}{{{E_{BKP}(k)} - {E_{DFT}(k)}}}^{2}}}$

where Nk is the number of selected k points in the extraction. The costfunction describes how much the guessed model parameters (γ1, γ2, γ3 andΔso) deviate from the DFT data.

In the fourth step, the cost function is iteratively reduced, by usingthe simplex optimization algorithm to optimize the model parameters (γ1,γ2, γ3 and Δso). In the iterative optimization of the model parameters,the second and third steps are repeated and the model parameters areupdated until convergence.

Various embodiments are directed to a different number of bands in thek.p model.

In the following, the bulk silicon six-band k.p model parameterextraction is used as an example, to show how the simplex optimizationalgorithm works in the extraction.

In this example, the calculation is done in the Nd-dimensional (Nd=4)parameter space, since there are four parameters to optimize. To startwith, (0, 0, 0, 0) is used as the initial guess of the model parameters(γ1, γ2, γ3 and Δso). A simplex with Nd+1 vertices Xi(x_(i1) ⁽⁰⁾, x_(i2)⁽⁰⁾, x_(i3) ⁽⁰⁾, x_(i4) ⁽⁰⁾) is formed surrounding the initial guess,where the superscript means the iteration step number and i=1, 2, . . ., Nd+1 is the vertex label. Then, the second and third steps areexecuted to obtain the cost function values (ci) for all vertices. Aftersorting, the vertex (Xm) with the largest cost function value (cm) willbe updated.

To update Xm, Xm is reflected with respect to the geometric average ofall other vertices, to obtain the reflected image Xr. Then, the costfunction value (cr) of Xr is evaluated using the second and third steps.According to the value of cr, the vertex is updated differently in thefollowing three different situations.

If min_(i≠m){c_(i)}≦c_(r)≦max_(i≠m){c_(i)},

Then the vertex Xm is updated as Xr.

If c_(r)≦min_(i≠m){c_(i)},

Then it means that the trial Xr is on the correct update direction inthe parameter space to reduce cost function but the reflection lengthmay be too short to be optimal. Then the reflection is extended by twiceas X′r whose cost function value is c′r. If c′r is smaller than cr, thevertex Xm is updated as X′r. If c′r is larger than cr, the vertex Xm isupdated as Xr.

If

c_(r)>max_(i≠m){c_(i)}

it means that the trial Xr is on the wrong update direction in theparameter space. Then the search direction is reversed as Xm−Xr, Thereversed search is repeated until c_(r)<max_(i≠m){c_(i)} is satisfied.

The above calculations continues iteratively until either the differencebetween the maximum cost function values of the two adjacent iterationsteps is smaller than a floor, e.g. 1 meV, or the maximum distancebetween any two vertices in the simplex is smaller than a floor, e.g.le-6.

Results can converge in a stepwise way to the experimentally measuredvalues, with a mismatch one the other of, for example, several percentin the final converged results, due to the fact that DFT results areapproximations of physical reality.

FIG. 3 is an example block diagram of simulation tools at multiplesimulation scales coupled together via an extraction tool using outputof a higher scale simulation tool as input for an ab initio simulationtool. To take advantage of the accuracy of more granular simulation, andthe lowered computation intensity of less granular simulation,parameters are passed between multiple levels of simulation. Suchembodiments provide data from simpler/large scale tools to the moresophisticated/small scale tools to accurately evaluate effects on themicroscopic scale.

Although the example discusses NEGF as the larger scale simulation tool,other embodiments are directed to other larger scale simulation toolsother than NEGF. Although NEGF and DFT are discussed, other modules canbe substituted.

At 36, results are produced from an intermediate scale IC simulationtool such as NEGF. At 34, results are processed into lower simulationscale input. Processing can be as minimal as passing a parameter, orperforming multiple operations to extract data. At 32, the simulation iscontinued using the results from the intermediate scale tool as input ofan ab initio simulation tool such as DFT.

The non-equilibrium Green's function (NEGF) is an important algorithm inthe TCAD tools and methodologies we propose here. The NEGF module can beused to simulate the transport properties of the devices, e.g. current,potential distribution, transmission coefficient, etc. Therefore, it isa vital part of the proposed TCAD tools.

The NEGF simulator is based on iterative self-consistent solution of theGreen's functions, the self-energies, and the potential profile. In theNEGF simulator, the calculation starts from the Hamiltonian matrix H,which can be obtained from either ab initio density functional theory(DFT) simulations, or tight binding parameterization, or effective massapproximation, or other techniques.

The steps are explained in more details below:

1. The contact self-energies are used to represent theelectrodes/contacts (like source and drain) that are linked to thetransport channel. It is evaluated iteratively at energy points ofinterests, by using exponentially converging contact self-energy Green'sfunction algorithms.

2. To start with, the potential profile is used as an initial guess ofthe final converged potential profile. The typical choice is a lineardrop from drain to source. Of course, other initial guess shapes areallowed. The principle of choosing the initial potential profile is thatit should be as close to the final converged potential profile aspossible, in order to reduce the iteration number and computational costto achieve convergence.

3. The retarded Green's function G^(r), the election Green's functionG^(n), and the hole Green's function G^(p) are evaluated at all energypoints of interests, by using numerical algorithms like (but not limitedto) matrix factorization, recursive Green's function algorithm, and theFast inverse using nested dissection, etc. The proposed approach usesefficient algorithms to accelerate the calculation by taking advantageof the special matrix structure of the Hamiltonian.

4. The in-scattering and out-scattering self-energies are computed byusing the Green's functions, which are computed in the previous step.These scattering self-energies are used to represent the variousscattering mechanism during transport.

5. The convergence check is performed to determine whether or not thecalculation of the scattering has converged. If no, more self-consistentcalculation loops will be performed. If yes, the calculation continuesto the next step.

6. Poisson's equation is calculated using the algorithms like, but notlimited to, direct matrix computation algorithms, iterative Krylovsubspace matrix computation algorithms, fast Fourier transform, and fastmultipole method, domain decomposition method, etc. The purpose is toobtain the updated potential profile from the known charge distribution.

7. The convergence check is performed to determine whether or not thepotential profile calculation has converged. If no, more iteration loopswill be performed. If yes, the calculation continues to the post-processmodule.

8. The post-process module calculates the physical quantities ofinterest, which includes (but not limited to), current density,current-voltage curve, transmission coefficient, density of states,potential profile, charge distribution, etc.

FIG. 4 is an example block diagram of simulation tools at multiplesimulation scales coupled together via intermediate tools to iteratebetween an ab initio simulation tool and a higher scale simulation tool.The block diagram of 42, 44, 46, 48, 50 and 52 essentially combinesFIGS. 2 and 3. In addition to one-way hierarchical modeling flow frommore sophisticated/small scale tools down to the simpler/large scaletools, one or several iterations can be performed by going in bothdirections along that hierarchy. Such feedback and iterations can beapplied across two or more levels of the model, potentially spanning therange from circuit/system level to the first principles level. To takeadvantage of the accuracy of more granular simulation, and the loweredcomputation intensity of less granular simulation, parameters are passedbetween multiple levels of simulation.

An iterative and self-adaptive scheme (mentioned as the “scheme”hereafter) of the parameterization process of the phenomenologicalsimulation modules and methodologies, is used to simulate thefabrication and operation of integrated circuit devices. The schemecombines the strengths of the ab initio simulation modules andmethodologies, which are comparatively more accurate but computationallyexpensive, and the merits of the phenomenological simulation modules andmethodologies, which are relatively less accurate but computationallyinexpensive, to offer a set of iterative, self-adaptive, and automatedsimulation and design tools and methodologies.

The “iterative parameterization” mentioned above covers multipledifferent categories of iterative processes. Iterative process (i)refers to the iterative parameter extraction between/among the modulesmentioned in the above two points. Iterative process (ii) refers to theiterative parameter extraction between the “top-down approach”, whichmeans that the physical quantities to be calculated are expressed asphenomenological equations with the phenomenological parametersextracted from the ab initio simulations, and the “bottom-up approach”,which means that the calculation starting point is the ab initioequations and the computational expenses are alleviated by approximatingsome computationally expensive components in the equations.

Although NEGF and DFT are discussed, other modules can be substituted.

In an iterative looped feedback, the NEGF module and the DFT module arecombined together to provide enhanced simulation capabilities, in twodirections. The NEGF module outputs non-equilibrium transport propertiesand electronic structure information, which are used in the DFT moduleto account for the non-equilibrium conditions. The DFT module outputsequilibrium electronic structure information, which is used in the NEGFmodule to simulate transport properties. These two directions iterate asa bi-directional feedback loop, to offer unprecedented TCAD simulationcapabilities. For example, to simulate the source-channel-drain devicestructure, the DFT module is first run to obtain the Hamiltonian andoverlap matrices. Then these matrices are input into the NEGF module tosimulate the transport properties. This generates the non-equilibriumelectron transport properties like potential distribution, which in turnis fed back into the DFT module to calculate physical properties likeforces on atoms and the internal stress under non-equilibriumconditions, etc.

Different types of an iterative process are as follows: (1) simulationfunctionality feedback; (2) calculation efficiency and precisionfeedback; and (3) the iterative looped feedback. Although NEGF and DFTare discussed, other modules can be substituted. They are introduced inthe three following sections below:

In the simulation functionality feedback, The NEGF module decides whatshould be calculated and sends instructions to the lower-level DFTmodule to get the computations done. For example, in the ab initioelectron transport simulation, the NEGF module uses ab initioHamiltonian matrix and overlap matrix as input. So the NEGF module sendsinstructions to the DFT module, requesting related calculations. In theeffective mass Hamiltonian electron transport calculations, the NEGFmodule can request the DFT module to perform band structure calculationsand extract the effective mass.

In the efficiency and precision feedback, the NEGF module runs electrontransport simulations and compares the results against benchmarkresults. The comparison is used to feedback into the DFT module, tostrike a good balance between the computational efficiency andprecision. For instance, the calculation is largely determined by thesize of the matrix that represents the system of interests. The largerthe matrix size, the more precise the results are. But the calculationwill be less efficient. In contrast, if the system is represented byusing smaller matrices, the calculation will be less precise, but thecalculation will be more efficient. By comparing against benchmarkresults and/or experimental calibrations of example systems, the NEGFmodule can work jointly with the lower-level DFT module, to determinethe optimum matrix size to represent the target system. By using thisoptimum matrix size, the simulation can achieve both good calculationprecision and high simulation efficiency.

The three processes introduced above are designed to be automated andself-adaptive, in order to minimize the human intervention and tomaximize productivity.

FIG. 5 is an example process flow of executing simulation toolsautomatically at multiple simulation scales, to improve inaccurate input(such as missing input).

Multiple simulation scales of various simulation modules, such as inFIG. 1, use output of one module as input for another module, andautomatically executing another module at the same simulation scale ordifferent simulation scale to improve inaccurate input (such as missinginput).

In the example of FIG. 1, if a particular simulation module has missinginput, the coordination module executes another module to provide themissing input. If a particular simulation scale is not specified in theexecution instruction, the coordination module determines theappropriate scales to run. The proposed modules receive targetsimulation quantities via a user interface, and instruct thecoordination module to start the simulation.

At 60, a user (or automated) instruction is received to begin simulationwithout specifying at last one simulation scale (or at least withoutspecifying one simulation tool). There are multiple options. In option62, simulation is initiated automatically at a particular simulationscale (or a particular simulation tool out of many) depending onsimulation input that does not specify the particular simulation scale(or depending on simulation input that does not specify does not specifythe particular simulation tool). In option 64, simulation is initiatedat a default simulation scale without regard to other simulation input(or initiated with a default simulation module without regard to othersimulation input), or with regard to an explicitly selected simulationscale (or with regard to an explicitly selected simulation module). At66, inaccurate parameters (such as missing parameters) are identified.At 68, simulation scales (or simulation tools) are automaticallyswitched to acquire inaccurate parameters such as missing parameters.

FIG. 6 shows different simulation volumes of simulation modules atdifferent simulation scales. A 3D simulation volume is indicated. Inother embodiments, the simulation volume may be 2D or 1D. Becausesimulator A has more granularity than simulator B, simulation volume A70 of simulator A is smaller than simulation volume B 72 of simulator B.Because simulation volume A 70 is smaller, the border between simulationvolumes A and B is also a border 70 of simulation volume A 70.

FIGS. 7-8 shows a switch between simulation modules at differentsimulation scales, from a larger simulation volume to a smallersimulation volume. In FIG. 7, nonzero simulated property 76 occupies arelatively small fraction of simulation volume B 72. In FIG. 8, nonzerosimulated property 76 occupies a relatively large fraction of simulationvolume A 70. Accordingly, the simulation modules/scales switchautomatically from simulation volume B 72 of simulator B to simulationvolume A 70 of simulator A.

FIGS. 9-10 shows a switch between simulation module volumes from asmaller simulation volume to a larger simulation volume. In FIG. 9,nonzero simulated property 76 is not fully captured by simulation volumeA 70. In FIG. 10, nonzero simulated property 76 occupies fits insimulation volume B 72. Accordingly, the simulation modules/scalesswitch automatically from simulation volume A 70 of simulator A tosimulation volume B 72 of simulator B.

Examples of a simulated property include: electrostatic potential,electric field, non-equilibrium charge distribution, stress distributionand stress gradient, strain distribution and strain gradient, electronand hole generation, electron and hole recombination, atomic migration(such as hydrogen, lattice atoms, and impurities), point defectformation, extended defect formation, void formation, ionic migration,filament formation, phase change (such as between crystal and amorphousstates), non-equilibrium spin distribution, electron and hole trappingat the defects, Joule heat generation, structure changes due to atomicand molecular chemical reactions, and optically generated electrons andholes. Such properties can be converted to DFT inputs.

FIGS. 11-12 show an error at the border between simulation modules atdifferent simulation scales, with horizontal and oblique asymptotes.

In the example of FIGS. 9-10, a nonzero simulated property was not fullycaptured by simulation volume A of simulator A, so the simulationmodules/scales switch automatically to simulation volume B 72 ofsimulator B. However, an alternative is to not switch and tolerate thenonzero error, remaining with simulation volume A of simulator A so longas the nonzero error does not exceed an error threshold.

FIG. 11 shows that at the border 74 between simulation volumes A and B,an error 82 exist in the nonzero simulated property 78. The nonzerosimulated property 78 has failed to reach the horizontally asymptoticvalue 80 of the nonzero simulated property 78. In FIG. 12, the nonzerosimulated property 78 has failed to reach the obliquely asymptotic value80 of the nonzero simulated property 78. So long as the error 82 doesnot does not exceed an error threshold, the nonzero error may betolerated by not switching from simulation volume A of simulator A tosimulation volume B 72 of simulator B.

FIGS. 13A, 13B, 13C and 13D illustrate various lattice configurations,as examples of arrangements in which a semiconductor property has afinite distortion range to be simulated as in FIGS. 6-12. The finitedistortion range can depend on the direction. Distortions can beelectrical, mechanical, or band structure. Examples include pointdefects such as vacancy defects, interstitial defects and substitutionaldefects, using a GaAs alloy as an example. A conventional 8-atom cell(e.g. 400), and a supercell composed of 4 conventional cells are shownin each of the figures. As used herein, a host is the material intowhich native defects and dopants diffuse, and a host atom is an atom inthe host material without any diffusion into the host material. The hostmaterial can be an alloy.

FIG. 13A illustrates a supercell 410 including host atoms Ga (Gallium)and As (Arsenic), and lattice vacancy defects (e.g. 411, 414) surroundedby adjacent host atoms Ga and As. A lattice vacancy defect refers to anatom site in a crystal lattice where a single host atom is missing.Neighbors of a point defect can be important. As shown in the example ofFIG. 13A, a vacancy defect has first order neighbors and second orderneighbors. For instance, vacancy defect 411 at an As site has 4first-order neighbors that are Ga atoms (e.g. 412), and moresecond-order neighbors (e.g. 413). Vacancy defect 414 at a Ga site has 4first-order neighbors that are As atoms (e.g. 415), and moresecond-order neighbors (e.g. 416).

In a different alloy there can be more options for first-orderneighbors. For instance in a SiGe alloy (not shown), a point defect suchas a vacancy defect can have different first-order neighbors including 4Si atoms, 3 Si atoms and 1 Ge atom, 2 Si atoms and 2 Ge atoms, 1 Si and3 Ge atoms, or 4 Ge atoms.

FIG. 13B illustrates an example of a dopant atom surrounded by variousdifferent numbers of host atoms adjacent thereto. Impurities or dopantscan be doped into the GaAs host material. Group IV elements such as Si(silicon) can act as either donors on Ga sites or acceptors on As sites.In the example of FIG. 13B, Si is used as the dopant (e.g. 425).

FIG. 13C illustrates an example of an interstitial defect atomsurrounded by various different numbers of host atoms adjacent thereto,where an interstitial defect atom is present in the interstitial spacesbetween the host crystal lattice sites. In an alloy (e.g. GaAs), eachalloying species (e.g. Ga, As) can be at a defect site between latticesites or an interstitial location off the crystal lattice. In theexample of FIG. 13C, a Ga interstitial is at a defect site (e.g. 435),while an As interstitial is at another defect site (e.g. 437). In atetrahedrally coordinated GaAs configuration (not shown), a Gainterstitial or a As interstitial can have four equidistant first-orderneighbors. In a hexagonally coordinated GaAs configuration (not shown),a Ga interstitial or a As interstitial can have six equidistantfirst-order neighbors, including 3 Ga atoms and 3 As atoms.

FIG. 13D illustrates an example of a substitutional defect atomsurrounded by various different numbers of host atoms adjacent thereto,where a host atom is replaced by an atom of a different type than thehost atoms. A substitutional defect atom can be smaller or larger than ahost atom (covalent radius of Ga=126 pm, covalent radius of As=119 pm).In the example of FIG. 13D, Be (Beryllium, covalent radius=90 pm) isshown as a smaller substitutional defect atom at a defect site (e.g.445), while Te (Tellurium, covalent radius=135 pm) is shown as a largersubstitutional defect atom at another defect site (e.g. 447).

For a more complex material, there can be more types of point defects.For instance, indium gallium arsenide (InGaAs) is a ternary alloy ofindium, gallium and arsenic. Indium and gallium are both from the borongroup (group III) of elements, and thus have similar roles in chemicalbonding. InGaAs is regarded as an alloy of gallium arsenide and indiumarsenide with properties intermediate between the two depending on theproportion of gallium to indium. For instance, compounds In0.75Ga0.25As,In0.5Ga0.5As, and In0.25Ga0.75 include different proportions of galliumto indium, while InAs does not include Ga and GaAs does include In.

In InGaAs, point defects can include As vacancy (i.e. missing latticeatom where As is supposed to be), In/Ga vacancy (i.e. missing latticeatom where In or Ga is supposed to be), As interstitial (i.e. extra Asatom between lattice sites), In interstitial (i.e. extra In atom betweenlattice sites), Ga interstitial (i.e. extra Ga atom between latticesites), As atom in the In/Ga lattice site, In atom in the As latticesite, and Ga atom in the As lattice site. For each of these pointdefects, there are different combinations of first-order neighbors,similar to the first-order neighbors described for the SiGe alloy.

FIG. 14 is a simplified block diagram of a computer system configured toperform IC simulation to implement any of the methods and processesherein.

Computer system 110 typically includes a processor subsystem 114 whichcommunicates with a number of peripheral devices via bus subsystem 112.These peripheral devices may include a storage subsystem 124, comprisinga memory subsystem 126 and a file storage subsystem 128, user interfaceinput devices 122, user interface output devices 120, and a networkinterface subsystem 116. The storage subsystem 128 includesnon-transitory memory storing computer programs, databases and otherresources to configure the data processing systems as tool forcontrolling multiple simulation tools at multiple simulation scales asdescribed herein. The tool can include an API configured to use inputparameter sets, and to perform the procedures of the tool using theinput parameter sets.

The input and output devices allow user interaction with computer system110. Network interface subsystem 116 provides an interface to outsidenetworks, including an interface to communication network 118, and iscoupled via communication network 118 to corresponding interface devicesin other computer systems. Communication network 118 may comprise manyinterconnected computer systems and communication links. Thesecommunication links may be wireline links, optical links, wirelesslinks, or any other mechanisms for communication of information, buttypically it is an IP-based communication network. While in oneembodiment, communication network 118 is the Internet, in otherembodiments, communication network 118 may be any suitable computernetwork.

The physical hardware component of network interfaces are sometimesreferred to as network interface cards (NICs), although they need not bein the form of cards: for instance they could be in the form ofintegrated circuits (ICs) and connectors fitted directly onto amotherboard, or in the form of macrocells fabricated on a singleintegrated circuit chip with other components of the computer system.

User interface input devices 122 may include a keyboard, pointingdevices such as a mouse, trackball, touchpad, or graphics tablet, ascanner, a touch screen incorporated into the display, audio inputdevices such as voice recognition systems, microphones, and other typesof input devices. In general, use of the term “input device” is intendedto include all possible types of devices and ways to input informationinto computer system 110 or onto computer network 118.

User interface output devices 120 may include a display subsystem, aprinter, a fax machine, or non visual displays such as audio outputdevices. The display subsystem may include a cathode ray tube (CRT), aflat panel device such as a liquid crystal display (LCD), a projectiondevice, or some other mechanism for creating a visible image. Thedisplay subsystem may also provide non visual display such as via audiooutput devices. In general, use of the term “output device” is intendedto include all possible types of devices and ways to output informationfrom computer system 110 to the user or to another machine or computersystem.

Storage subsystem 124 stores the basic programming and data constructsthat provide the functionality of certain embodiments of the presentinvention. For example, the various modules implementing thefunctionality of certain embodiments of the invention may be stored instorage subsystem 124. These software modules are generally executed byprocessor subsystem 114.

Memory subsystem 126 typically includes a number of memories including amain random access memory (RAM) 130 for storage of instructions and dataduring program execution and a read only memory (ROM) 132 in which fixedinstructions are stored. File storage subsystem 128 provides persistentstorage for program and data files, and may include a hard disk drive, afloppy disk drive along with associated removable media, a CD ROM drive,an optical drive, or removable media cartridges. The databases andmodules implementing the functionality of certain embodiments of theinvention may have been provided on a computer readable medium such asone or more CD-ROMs, and may be stored by file storage subsystem 128.The host memory 126 contains, among other things, computer instructionswhich, when executed by the processor subsystem 114, cause the computersystem to operate or perform functions as described herein. As usedherein, processes and software that are said to run in or on “the host”or “the computer”, execute on the processor subsystem 114 in response tocomputer instructions and data in the host memory subsystem 126including any other local or remote storage for such instructions anddata.

Bus subsystem 112 provides a mechanism for letting the variouscomponents and subsystems of computer system 110 communicate with eachother as intended. Although bus subsystem 112 is shown schematically asa single bus, alternative embodiments of the bus subsystem may usemultiple busses.

Computer system 110 itself can be of varying types including a personalcomputer, a portable computer, a workstation, a computer terminal, anetwork computer, a television, a mainframe, a server farm, or any otherdata processing system or user device. Due to the ever changing natureof computers and networks, the description of computer system 110 isintended only as a specific example for purposes of illustrating thepreferred embodiments of the present invention. Many otherconfigurations of computer system 110 are possible having more or lesscomponents than the computer system.

In addition, while the present invention has been described in thecontext of a fully functioning data processing system, those of ordinaryskill in the art will appreciate that the processes herein are capableof being distributed in the form of a computer readable medium ofinstructions and data and that the invention applies equally regardlessof the particular type of signal bearing media actually used to carryout the distribution. As used herein, a computer readable medium is oneon which information can be stored and read by a computer system.Examples include a floppy disk, a hard disk drive, a RAM, a CD, a DVD,flash memory, a USB drive, and so on. The computer readable medium maystore information in coded formats that are decoded for actual use in aparticular data processing system. A single computer readable medium, asthe term is used herein, may also include more than one physical item,such as a plurality of CD ROMs or a plurality of segments of RAM, or acombination of several different kinds of media. As used herein, theterm does not include mere time varying signals in which the informationis encoded in the way the signal varies over time.

FIG. 15 illustrates EDA tools and process flow for integrated circuitdesign and manufacturing.

Aspects of the invention can be used to support an integrated circuitdesign flow. At a high level, the process starts with the product idea(step 200) and is realized in an EDA (Electronic Design Automation)software design process (step 210). When the design is finalized, it canbe taped-out (step 227). At some point after tape out, the fabricationprocess (step 250) and packaging and assembly processes (step 260) occurresulting, ultimately, in finished integrated circuit chips (result270).

The EDA software design process (step 210) is itself composed of anumber of steps 212-230, shown in linear fashion for simplicity. In anactual integrated circuit design process, the particular design mighthave to go back through steps until certain tests are passed. Similarly,in any actual design process, these steps may occur in different ordersand combinations. This description is therefore provided by way ofcontext and general explanation rather than as a specific, orrecommended, design flow for a particular integrated circuit.

A brief description of the component steps of the EDA software designprocess (step 210) will now be provided.

System design (step 212): The designers describe the functionality thatthey want to implement, they can perform what-if planning to refinefunctionality, check costs, etc. Hardware-software architecturepartitioning can occur at this stage. Example EDA software products fromSynopsys, Inc. that can be used at this step include Model Architect,Saber, System Studio, and DesignWare® products.

Logic design and functional verification (step 214): At this stage, theVHDL or Verilog code for modules in the system is written and the designis checked for functional accuracy. More specifically, the design ischecked to ensure that it produces correct outputs in response toparticular input stimuli. Example EDA software products from Synopsys,Inc. that can be used at this step include VCS, VERA, DesignWare®,Magellan, Formality, ESP and LEDA products.

Synthesis and design for test (step 216): Here, the VHDL/Verilog istranslated to a netlist. The netlist can be optimized for the targettechnology. Additionally, the design and implementation of tests topermit checking of the finished chip occurs. Example EDA softwareproducts from Synopsys, Inc. that can be used at this step includeDesign Compiler®, Physical Compiler, DFT Compiler, Power Compiler, FPGACompiler, TetraMA1, and DesignWare® products.

Netlist verification (step 218): At this step, the netlist is checkedfor compliance with timing constraints and for correspondence with theVHDL/Verilog source code. Example EDA software products from Synopsys,Inc. that can be used at this step include Formality, PrimeTime, and VCSproducts.

Design planning (step 220): Here, an overall floor plan for the chip isconstructed and analyzed for timing and top-level routing. Example EDAsoftware products from Synopsys, Inc. that can be used at this stepinclude Astro and Custom Designer products.

Physical implementation (step 222): The placement (positioning ofcircuit elements) and routing (connection of the same) occurs at thisstep, as can selection of library cells to perform specified logicfunctions. Example EDA software products from Synopsys, Inc. that can beused at this step include the Astro, IC Compiler, and Custom Designerproducts.

Analysis and extraction (step 224): At this step, the circuit functionis verified at a transistor level, this in turn permits what-ifrefinement. Example EDA software products from Synopsys, Inc. that canbe used at this step include AstroRail, PrimeRail, PrimeTime, andStar-RC1T products.

Physical verification (step 226): At this step various checkingfunctions are performed to ensure correctness for: manufacturing,electrical issues, lithographic issues, and circuitry. Example EDAsoftware products from Synopsys, Inc. that can be used at this stepinclude the Hercules product.

Tape-out (step 227): This step provides the “tape out” data to be used(after lithographic enhancements are applied if appropriate) forproduction of masks for lithographic use to produce finished chips.Example EDA software products from Synopsys, Inc. that can be used atthis step include the IC Compiler and Custom Designer families ofproducts.

Resolution enhancement (step 228): This step involves geometricmanipulations of the layout to improve manufacturability of the design.Example EDA software products from Synopsys, Inc. that can be used atthis step include Proteus, ProteusAF, and PSMGen products.

Mask data preparation (step 230): This step provides mask-making-ready“tape-out” data for production of masks for lithographic use to producefinished chips. Example EDA software products from Synopsys, Inc. thatcan be used at this step include the CATS(R) family of products.

Parallel flow. The integrated circuit manufacturing flow includes aparallel flow, as follows:

(1) Develop individual process steps for manufacturing the integratedcircuit. This can be modeled with EDA tools such as the Synopsys tools“Sentaurus Process”, “Sentaurus Topography”, and “SentaurusLithography”. The input information here is the process conditions liketemperature, reactor ambient, implant energy, etc. The outputinformation is the change in geometry or doping profiles or stressdistribution.

(2) Integrate the individual process steps into the complete processflow. This can be modeled with EDA tools such as the Synopsys tool“Sentaurus Process”. The input information here is the collection of theprocess steps in the appropriate sequence. The output is the geometry,the doping profiles, and the stress distribution for the transistors andthe space in between the transistors.

(3) Analyze performance of the transistor manufactured with this processflow. This can be done with EDA tools such as the Synopsys tool“Sentaurus Device”. The input information here is the output of step (3)and the biases applied to transistor terminals. The output informationis the currents and capacitances for each bias combination. For siliconbased processes or structures, much of the information about thematerials needed for simulation of electrical behavior using these toolsis well known. For other materials, it may be necessary to generate orprovide parameters like lattice structure, diffusivity and concentrationof defects, and the like in order to support device and process scalesimulations. An EDA tool for generating parameters like this isdescribed herein.

(4) If necessary, modify the process steps and the process flow toachieve the desired transistor performance. This can be done iterativelyby using tools such as the Synopsys tools mentioned above.

Once the process flow is ready, it can be used for manufacturingmultiple circuit designs coming from different fabless companies. TheEDA flow 212-230 will be used by such fabless companies. The parallelflow described here is used at a foundry to develop a process flow thatcan be used to manufacture designs coming from their fabless customers.A combination of the process flow and the masks 230 are used tomanufacture any particular circuit. If the integrated circuit ismanufactured at an IDM (integrated device manufacturer) company insteadof the combination of a fables company and a foundry, then both parallelflows described above are done at the same IDM company.

There is also a bridge between these tools and the 212-230 EDA tools.The bridge can be an EDA tool a Synopsys tool “Seismos” that appliescompact proximity models for particular circuit design and layout toobtain netlist with instance parameters for each individual transistorin the circuit as a function of its neighborhood and stress, includingmaterial conversion stress.

Incorporated by reference herein are the following documents, whichprovide additional information about terms and components referencedherein:

-   Mathieu Luisier, “Quantum Transport for Engineers Lecture 4: Wave    Function (WF) formalism and electrostatics”, Integrated Systems    Laboratory, ETH Zurich (2012).-   Kyoung-Youm Kim and Byoungho Lee, “Quantum transport modeling in    anisotropic semiconductors using Wigner function formulation”,    Proceedings Conference on Optoelectronic and Microelectronic    Materials and Devices, COMMAD 2000. (2000)-   Daniel Arovas, “Lecture Notes on Condensed Matter Physics, Chapter 1    Boltzmann Transport”, Department of Physics, University of    California, San Diego (2010).-   R. Grau-Crespo, “Electronic structure and magnetic coupling in    FeSbO4: A DFT study using hybrid functionals and GGA+U methods”,    PHYSICAL REVIEW B 73, (2006).-   Michel Côté, “Introduction to DFT+U”, International Summer School on    Numerical Methods for Correlated Systems in Condensed Matter,    Université de Montréal.-   A. Muramatsu, “Quantum Monte Carlo for lattice fermions”, in: M. P.    Nightingale, C. J. Umriga (Eds.), Proceedings of the NATO Advanced    Study Institute on Quantum Monte Carlo Methods in Physics and    Chemistry, Kluwer Academic Publishers, 1999.-   E. K. U. Gross and N. T. Maitra, “Introduction to TDDFT”, Chapter in    Fundamentals of Time-Dependent Density Functional Theory,    Springer-Verlag 2012.-   M. A. L. Marques, E. K. U. Gross, Time-dependent density functional    theory, in: C. Fiolhais, F. Nogueira, M. A. L. Marques (Eds.), A    Primer in Density Functional Theory, Springer Lecture Notes in    Physics, vol. 620, Springer 2003, pp. 144-184.-   D. A. Ryndyk, “Tight-binding model”, Lectures 2006-2007, Dresden    University of Technology.-   R. E. Bank, “Numerical Methods for Semiconductor Device Simulation”,    IEEE Transactions on Electron Devices, Vol. ED-30, No. 9, 1983.-   J. F. Lee, “Time-Domain Finite-Element Methods”, IEEE Transactions    on Antenna and Propagation, Vol. 45, NO. 3, 1997.-   R. Eymard, “Finite Volume Methods”, course at the University of    Wroclaw, 2008.-   X. L. Chen, “An advanced 3D boundary element method for    characterizations of composite materials”, Engineering Analysis with    Boundary Elements 29, 513-523 (2005).-   D. Marx, “Ab initio molecular dynamics: Theory and Implementation”,    Modern Methods and Algorithms of Quantum Chemistry, J. Grotendorst    (Ed.), John von Neumann Institute for Computing, Julich, {umlaut    over ( )}NIC Series, Vol. 1, 2000.-   BURKE, K., et al., “The ABC of DFT” (2007), which among other things    describes DFT.-   KRESSE, G., et. al., VASP the Guide (Sep. 9, 2013).

The invention claimed is:
 1. An EDA tool comprising: a data processor; storage configured to provide computer program instructions to the processor, including: a controller module causing a plurality of simulation modules to perform an EDA simulation at a plurality of different simulation scales, the plurality of simulation modules including: a first set of one or more ab initio simulation modules simulating a first volume with a first boundary; and a second set of one of more non-ab initio simulation modules simulating a second volume with a second boundary, the second volume larger than the first volume, wherein the controller module causes, responsive to a simulated volume occupied by a nonzero part of a simulated property being a larger percentage of the second volume than the first volume, switching from the second set of one or more non-ab initio simulation modules to the first set of one of more ab initio simulation modules.
 2. The EDA tool of claim 1, wherein the simulated property as simulated by the first set of one or more ab initio simulation modules is equal at the first boundary to an asymptotic value of the simulated property.
 3. The EDA tool of claim 1, wherein the simulated property as simulated by the second set of one or more ab initio simulation modules is equal at the second boundary to an asymptotic value of the simulated property.
 4. The EDA tool of claim 1, wherein the simulated volume fits within the first volume.
 5. The EDA tool of claim 1, wherein the first set of one or more simulation modules includes a density functional theory module, and the second set of one or more simulation modules excludes the density functional theory module.
 6. A computer-implemented method comprising: causing a plurality of simulation modules to perform an EDA simulation at a plurality of different simulation scales, the plurality of simulation modules including: a first set of one or more ab initio simulation modules simulating a first volume with a first boundary; and a second set of one of more non-ab initio simulation modules simulating a second volume with a second boundary, the second volume larger than the first volume; and causing, responsive to a simulated volume occupied by a nonzero part of a simulated property being a larger percentage of the second volume than the first volume, switching from the second set of one or more non-ab initio simulation modules to the first set of one of more ab initio simulation modules.
 7. The computer-implemented method of claim 6, wherein the simulated property as simulated by the first set of one or more ab initio simulation modules is equal at the first boundary to an asymptotic value of the simulated property.
 8. The computer-implemented method of claim 6, wherein the simulated property as simulated by the second set of one or more ab initio simulation modules is equal at the second boundary to an asymptotic value of the simulated property.
 9. The computer-implemented method of claim 6, wherein the simulated volume fits within the first volume.
 10. The computer-implemented method of claim 6, wherein the first set of one or more simulation modules includes a density functional theory module, and the second set of one or more simulation modules excludes the density functional theory module.
 11. An EDA tool comprising: a data processor; storage configured to provide computer program instructions to the processor, including: a controller module causing a plurality of simulation modules to perform an EDA simulation at a plurality of different simulation scales, the plurality of simulation modules including: a first set of one or more ab initio simulation modules of a first volume with a first boundary; and a second set of one of more non-ab initio simulation modules of a second volume with a second boundary, the second volume larger than the first volume, wherein the controller module causes the first set of one or more ab initio simulation modules to perform the EDA simulation of a simulated property, and depending on whether a nonzero magnitude of an error of the simulated property exceeds an error threshold, the controller module causing one of: (i) switching from the first set of one or more ab initio simulation modules to the second set of one of more non-ab initio simulation modules, and (ii) remaining with the first set of one or more ab initio simulation modules despite the error.
 12. The EDA tool of claim 11, wherein the error is a nonzero difference between: (i) the simulated property at the first boundary simulated by the first set of one or more ab initio simulation modules, and (ii) an asymptotic value of the simulated property beyond the first boundary.
 13. The EDA tool of claim 11, wherein the asymptotic value is obliquely asymptotic.
 14. The EDA tool of claim 11, wherein the asymptotic value is horizontally asymptotic.
 15. The EDA tool of claim 11, wherein the asymptotic value is vertically asymptotic.
 16. The EDA tool of claim 11, wherein the first set of one or more simulation modules includes a density functional theory module, and the second set of one or more simulation modules excludes the density functional theory module.
 17. A computer-implemented method comprising: causing a plurality of simulation modules to perform an EDA simulation at a plurality of different simulation scales, the plurality of simulation modules including: a first set of one or more ab initio simulation modules of a first volume with a first boundary; and a second set of one of more non-ab initio simulation modules of a second volume with a second boundary, the second volume larger than the first volume; and causing the first set of one or more ab initio simulation modules to perform the EDA simulation of a simulated property, and depending on whether a nonzero magnitude of an error of the simulated property exceeds an error threshold, causing one of: (i) switching from the first set of one or more ab initio simulation modules to the second set of one of more non-ab initio simulation modules, and (ii) remaining with the first set of one or more ab initio simulation modules despite the error.
 18. The computer-implemented method of claim 17, wherein the error is a nonzero difference between: (i) the simulated property at the first boundary simulated by the first set of one or more ab initio simulation modules, and (ii) an asymptotic value of the simulated property beyond the first boundary.
 19. The computer-implemented method of claim 17, wherein the asymptotic value is obliquely asymptotic.
 20. The computer-implemented method of claim 17, wherein the asymptotic value is horizontally asymptotic.
 21. The computer-implemented method of claim 17, wherein the asymptotic value is vertically asymptotic.
 22. The computer-implemented method of claim 17, wherein the first set of one or more simulation modules includes a density functional theory module, and the second set of one or more simulation modules excludes the density functional theory module. 